a) I, ii, (133-138) "O, that this too too sullied flesh would melt/ Thaw, and resolve itself into a dew/ Or that the Everlasting had not fixed/ His canon 'gainst (self-slaughter!) O God, God/ How (weary,) stale, flat and unprofitable/ Seem to me all the uses of this world!"
-Hamlet's thoughts of his flesh melting into dew is somewhat suicidal after the death of his father and his mother remarrying.
b) I, ii, (161-162) "O, most wicked speed, to post/ With such dexterity to incestuous sheets!"
-This quote is addressing his mother's marriage to Hamlet's uncle after King Hamlet's death. This seems to be on the sane side of the spectrum because it would be normal to have these thoughts.
c) I, iv, (190-192) "How strange or odd some'er I bear myself/ (As I perchance hereafter shall think meet/ To put an antic disposition on".
-This is where Hamlet says that he shall put on an "attention getting, funny" disposition on. This turns the whole perspective of the novel around. Does Hamlet pretend to be batty around everyone? Or did he fake so much that he started to actually go mad?
